> Hello,
>
> currently investigating nbackup reliability/bugs. CORE-2648 is marked as
> fixed in 2.1.4 and CORE-3521, which is currently open, seems to like
> similar (forced writes vs. flushing to disc).
>
> How do they differ?
CORE-2648 set FW mode for delta file in the same value as of main database
file.
CORE-3521 flushed delta file buffers when main database files buffers are
flushed.
This is different things. FW mode defines how OS file cache will handle
writes.
When FW is OFF then file system free to accumulate writes in file cache and do
actual writes when OS think it is necessary\feasible. When FW is ON then file
system still cached data pages but not delayed physical writes to disk.
Flushing is different thing. It instructs OS to write all dirty cached
buffers of given file
immediately. Firebird calls flush every time some transaction is finished and
on disconnect
(look also at MaxUnflushedWrites and MaxUnflushedWriteTime settings at
firebird.conf).
Note, when FW is ON then OS shouldn't have dirty buffers and Firebird do not
flushed its files.
So, before CORE-2648 was fixed, delta file was always opened in FW=OFF mode
despite of database settings. Before CORE-3521 was fixed delta file contents
was not
flushed to disk when transactions finished.
Hope it is clear,
Vlad
PS CORE-3521 is not marked as fixed because it is not backported into 2.1.5
still.
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